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CONNECTIONS – PLUMBING
RELIEF VALVE DRAIN
DN15 copper drain lines must be fitted to the temperature pressure relief valve
and expansion control valve (if one is installed) to carry the discharge clear of
the water heater. Connect the drain lines to the valves using disconnection
unions. The drain line from the valve to the point of discharge should be as short
as possible, have a continuous fall all the way from the water heater to the
discharge outlet and have no tap, valves or other restrictions in the pipe work. A
drain line from a relief valve must comply with the requirements of
AS/NZS 3500.4 and Clause G12 of the New Zealand Building Code.
The length of the drain line in metres plus the number of changes in direction
must not exceed twelve (12). For example a drain line nine (9) metres in length
can have no more than three bends before discharging at an outlet or air gap.
The length of a drain line is to be reduced by one (1) metre for each additional
bend required. Where the distance in metres and number of changes in direction
to the point of final discharge exceeds twelve (12), the drain line can discharge
into a tundish.
In New Zealand the drain lines from the temperature pressure relief valve and
expansion control valve from an individual water heater may be interconnected
where freezing is unlikely to occur. The combined drain line must have a
minimum size of DN20 and discharge via a minimum air gap of a minimum
25 mm.
The outlet of a drain line must be in such a position that flow out of the pipe can
be easily seen, but arranged so discharge will not cause injury, damage or
nuisance. The termination point of a drain line must comply with the requirements
of AS/NZS 3500.4. Drain lines must not discharge into a safe tray.
In locations where water pipes are prone to freezing, drain lines must be
insulated, must not exceed 100 mm in length and are to discharge into a tundish
through an air gap of a minimum 25 mm.
If a drain line discharges into a tundish, the drain line from the tundish must be
not less than DN20 and one size larger than drain line from the relief valve(s).
The drain line from a tundish must meet the same requirements as for a drain
line from a relief valve.
Warning: As the function of the temperature pressure relief valve on this
water heater is to discharge high temperature water under certain conditions, it
is strongly recommended the pipe work downstream of the relief valve be
capable of carrying water exceeding 93°C. Failure to observe this precaution
may result in damage to pipe work and property.
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